1. Field of the Invention
This invention relates generally to air conditioning, and more particularly to a heater-cooler of air in cabs and compartments of vehicles.
The invention can also be used for heating and cooling air in production spaces and living rooms.
2. Description of the Related Art
There are known heaters for heating the incoming air and the cab of a vehicle, in which highly efficient heat transfer elements are used. These elements function according to the principle of closed evaporation-condensation cycle. The working liquid is returned from the condensation zone to the evaporation zone along a capillary structure under the action of capillary forces (such heat transfer elements are known as thermal tubes), or only along the shell wall of the element under the action of forces of gravity (two-phase thermal siphons). The heat transfer elements are accommodated in the housing of the heater and extend through a vertical or horizontal partition dividing the housing into sections for the passage of air being heated and a heat transfer agent being utilized (such as exhaust gases, hot liquid, used hot air, etc.).
A major disadvantage of these prior art apparatus resides in that they fail to cool air in the summer time of year, and therefore fail to provide comfort conditions for the driver of the vehicle. In addition, such heaters convey to the cab warm dry air of a humidity insufficient to provide comfort for the driver.
There are also known apparatus for cooling air conveyed to the cab of a vehicle through efficient evaporation of a liquid. Such apparatus include evaporative, indirect evaporative, and regeneration indirect evaporative air cooling systems.
One disadvantage of air coolers of evaporative and indirect evaporative type is the low degree to which the air is cooled. Apparatus of the regeneration indirect evaporative type are free from the above disadvantage, although, as the other aforedescribed coolers, they are not capable of heating air in summer the winter time and therefore fail to ensure comfort conditions in the cab of a vehicle.
There is further known an apparatus for heating and cooling air in the cab of a vehicle, which comprises a housing divided by a horizontal partition into two sections, viz. upper and lower sections, trays for water in the lower section, thermal tubes secured vertically in the partition with an outer surface of the lower ends of these tubes lined with a capillary porous material in contact with water, and a port in the horizontal partition having a controllable gate to communicate the outlet part of the upper section with the inlet of the lower section. This apparatus operates as follows. In summer time the incoming flow of hot air passes through the upper section to be split at the outlet therefrom into two flows. The first flow is directed to the cab, whereas the other flow is conveyed through the port in the partition to the lower section, where it is passed over the moist capillary porous material to cause evaporation of moisture, whereby the lower ends of the thermal tubes are cooled, and the working substance present inside the thermal tubes is condensed. The condensate flows along the capillary structure to the upper ends of the thermal tubes to boil out and thereby withdraw heat from the hot air. The cooled air is conveyed to the cab (first flow) and to the lower section (second flow), whereas vapors of the working substance enter the lower ends of the thermal tubes, where they are condensed, after which the cycle is repeated. In winter time of year the port in the partition is closed by the gate, and no water is present in the tray. Exhaust gases from the engine of the vehicle are conveyed to the lower section to pass over the ends of the thermal tubes and cause boiling of the working substance, which in the form of vapors enter the upper ends of the thermal tubes to be condensed and transfer heat to the flow of cold air passing through the upper section. The flow of atmospheric air is heated and conveyed to the cab.
This invention materializing the principle of regenerative indirect evaporation cooling is free of a number of disadvantages inherent in the previously described apparatus, because a single unit ensures both heating the air (in winter) and cooling (in summer) providing comfort conditions for the driver in any time of year. However, expanding the functional capabilities of this apparatus resulted in a number of disadvantages.
A major disadvantage of this known heater-cooler resides in that the second (humidified) air flow is conveyed in summer through the same section (vz., lower section) as is the flow of exhaust gases in winter. In winter this invariably affects wettability of the capillary porous material, followed by clogging of the pores with combustion products, and eventually in summer to fast corrosion of the capillary porous material and housing of thermal tubes caused by acid solutions produced by water-dissolved oxides of the elements present in the combustion products (in the pores of the material). Clogged pores of the capillary porous material fail to provide sufficient wetting and elevation of water to the height of the lower ends of the thermal tubes. Therefore, this apparatus is not sufficiently reliable in operation, and has a rather short service life.
The above apparatus features low heat and cold generation capacity, that is capacity related to the unit volume of the apparatus, due to low efficiency of the processes of heat and mass transfer in the sections. Such low efficiency is caused by small heat and mass exchange surface, since the thermal tubes have smooth walls, and the porous lining is provided at the outer insufficient surface area of the housing of the thermal tubes.
In the cold time of year heating of air in the known apparatus is accompanied by a sudden drop in the relative humidity of air. For example, heating of air from minus 10.degree. C. (even at a very high relative humidity of 90%) to plus 20.degree. C. is accompanied by a reduction in its relative humidity to 10%, which is substantially below comfort humidity of air which normally must be not less than 50%.
Another disadvantage is the vertical positioning of the thermal tubes in the horizontal partition, since during cooling air in summer the thermal tubes operate in rather unfavorable antigravity conditions (the working liquid moves along the capillaries from the lower ends of the thermal tubes to the upper ends in a direction counter to the gravity forces). This in turn substantially reduces the heat transfer capacity of the thermal tubes, as compared with the horizontal tube arrangement, which affects the efficiency of the apparatus.
Further, this known apparatus is difficult to service and repair because, firstly, it requires frequent and periodic cleaning of the capillary porous material from contaminants including products of combustion, or complete removal of such material followed by the application of new porous material, and secondly, water tends to evaporate from the tray, and the driver is obliged to periodically replenish it.